Mariam Crow and Kathleen Stitzlein's device tests saliva to determine the concentration of pot's active chemical in the bloodstream. Police must now wait weeks to get results from blood tests for marijuana use.

The two women recently received a $10,000 inventors' award. They previously received Ohio Third Frontier funding to develop their device, which they are calling the Cannibuster.

Recreational use of marijuana in a growing number of states is prompting law enforcement agencies to look more closely at pot smoking drivers, reported the Associated Press.

Studies of marijuana's effects show that the drug can slow decision-making, decrease peripheral vision and impede multitasking, all of which are critical driving skills. But unlike with alcohol, drivers high on pot tend to be aware that they are impaired and they try to compensate by driving slowly, avoiding risky actions such as passing other cars, and allowing extra room between vehicles.

On the other hand, combining marijuana with alcohol appears to eliminate the pot smoker's exaggerated caution and it seems to increase driving impairment beyond the effects of either substance alone.

"We see the legalization of marijuana in Colorado and Washington as a wake-up call for all of us in highway safety," said Jonathan Adkins, executive director of Governors Highway Safety Association, which represents state highway safety offices."We don't know enough about the scope of marijuana-impaired driving to call it a big or small problem. But anytime a driver has their ability impaired, it is a problem."